1. Technical Field
The present invention relates to a projection lens which enlarges and displays display information from a light valve such as liquid crystal display element, and particularly to a projection lens suitable for a front type projection type display device and a projection type display device using the same.
2. Related Art
Recently, a projection type display device using a light valve such as a liquid crystal display device or a DMD display device has been widely spread. Particularly, there has been widely used a projection type display device which uses three light valves so that the three light values correspond respectively to illumination light of RGB primaries, thereby to modulate these respective illumination light, synthesizes the light modulated by the respective light valves by means of a prism or the like, and displays an image on a screen through a projection lens.
The projection lens mounted on such the projection type display device which synthesizes the respective modulation light from the three light valves by the color-synthesized optical system and projects the synthesized light. So the projection lens requires a large back focal length in order to arrange the prism for performing color synthesis as described above and in order to avoid a thermal problem. Further, since spectral characteristic in the color-synthesized optical system changes by an angle of the incident light, it is necessary for the projection lens to have a characteristic that the entrance pupil seen from the reduction side is located far enough, that is, telecentricity. Further, it is required that the projection lens is a fast lens and aberrations are corrected in accordance with resolution of the light valve.
As projection lenses which satisfy such the demands to some degree, those disclosed in, for example, the following Patent Documents 1 (JP-A-2003-015033 corresponding to U.S. Pat. No. 6,624,952) and Patent Document 2 (JP-A-2004-326079 corresponding to U.S. Pat. No. 6,947,222) have been known. Further, this applicant has already disclosed such the projection lens to the Japanese Patent Office (refer to the following Patent Document 3 (Japanese Patent Application No. 2007-157248)).
The projection lenses described in these Patent Documents are wide-angle lenses in which an angle of view is 100 degrees or more.
As the projection type display device, there have been known a front type device which has a projection lens arranged on the same side as the viewer side in relation to a screen and images the light emitted from the projection lens on a reflection type screen, and a rear type device which has a projection lens arranged so as to interpose a screen between a viewer and the projection lens and images the light emitted from the projection lens on a transmission type screen.
In the rear type projection type display device of their types, there has been known well such the construction that parts from a light source to a screen are accommodated in a cabinet like a rear projection television, and that the light carrying picture information is projected toward the screen disposed in front of the cabinet from a projection lens disposed in a back of the cabinet. The projection lenses disclosed in the above Patent Documents 1 to 3 assume that they are mounted on such the rear type projection type display device.
However, in such the projection lens in the rear type device, in order to reduce the thickness of the cabinet, a prism or a mirror for turning back an optical axis is arranged in a lens system, and a full lens length along the optical axis becomes long, so that increase in spatial size of the device is caused. Accordingly, in case that the projection lenses described in the above Patent Documents are used in the front type projection type display device, there is a problem that compactification of the device size cannot be realized.
Further, the front type projection type display system (including the display device and the screen), compared with the rear type, has limits in size of installation space of the system. Therefore, it is desired that the working distance from the display device to the screen is shorten, and it is required that a wider viewing angle of the projection lens is realized.
The invention has been made in view of such circumstances, and its object is to provide a high-resolution projection lens which has the reduction side constituted telecentrically and a back focal length suitable to recent projection lenses, and is capable of realizing compactification and a wider viewing angle as the entirety of a lens system so that this lens can be applied also to a projection lens in a front type projection type display device; and to provide a projection type display device using this projection lens.